1. Field of the Invention
The present invention relates to heat pipes and, in particular, to such heat pipes which are switchable from a condition where no heat is transferred to that where full heat transfer at a predetermined temperature occurs.
2. Description of the Prior Art
It is sometimes desired and at times required to have a sharp demarcation between full and no transfer of heat to a heat sink at a specific operating temperature. For example, certain electronic components, such as diodes and gun devices, operate best at a constant temperature. At lower temperatures their output is less than optimal, and at higher temperatures they may be damaged. To prevent such overheating, they are generally coupled to a heat sink; however the thermal connection slows their heating and therefore increases the time in which they become fully operative. It is therefore desirable that such electronic components be insulated from their heat sink to permit the fastest possible warm up and, as soon as they reach their operating temperature, a thermal coupling is made to maintain them at a constant operating temperature.
Known devices for controlling temperature are described in U.S. Pat. Nos. 3,563,309 and 3,651,865. These heat pipes operate on the variable conductance heat pipe (VCHP) principle. Inert gas as well as working fluid are sealed within the heat pipe for temperature control. There is heat transfer at all times to a greater or lesser extent. Therefore, there is no demarcation point between thermal insulation and thermal conductivity, in accordance with the above desire or requirement.